Butyric acid fermentation from pretreated and hydrolyzed wheat straw by C.tyrobutyricum

Butyric acid fermentation has long been discussed in the last decade due to the wide application of butyric acid in chemical, pharmaceutical and food industries. Among other microbial strains, C.tyrobutyricum was found interesting due to its higher yield (more than 93% of the theoretical yield) and higher productivity. However, very few studies have focused on fermentation of sugars derived from lignocellulogic biomass. The present study investigates butyric acid fermentation from pretreated and enzymatically hydrolyzed wheat straw. The sugars derived from wheat straw consist mainly of glucose and xylose at a concentration of 71,6±0,2 g/l and 55,4±0,2 g/l respectively, with TS content 20,87% (g/g). From an economical point of view, the conversion of both sugars is very important. In fact C.tyrobutyricum has the capability to convert both hexose and pentose sugars. Results from batch experiments with C.tyrobutyricum showed that the strain was capable of producing butyric acid from hydrolyzed wheat straw by simultaneous uptake of glucose and xylose. Maximum yield of butyric acid (0,47g/g sugars, 96% of the theoretical yield) was obtained at a pH between 6 and 7 with higher selectivity (>90%). However, the xylose uptake rate was much lower than that of glucose, implying that further process development is required. Moreover, reduced cell growth rate was observed at higher metal (K+) concentration added during pH control which could be overcome by in-situ separation of butyric acid.